How do we propose addressing Traffic Noise Concerns?
SCDOT conducted a detailed noise analysis of the project to understand existing and future noise levels. If the existing or future noise levels exceeded a level defined by the Federal Highway Administration as a noise impact, we considered how those noise levels might be reduced through the construction of a noise barrier. The following factors were considered as part of the noise barrier evaluation:
Is the noise wall technically feasible?
How effective is the noise barrier at reducing noise levels? Will noise barrier effectively reduce noise levels for the majority of residents behind the barrier?
And finally, how much would the noise barrier cost to construct? Is the cost of the noise barrier a reasonable expenditure relative to anticipated reduction in noise levels?
This analysis led us to identify the potential noise walls outlined in the interactive noise wall map below. As the next step, public preference for or against a wall will be obtained through a balloting process among adjacent property owners and tenants.
There are many ways to reduce noise. Noise walls are one tool, but berms and highway design can help reduce noise as well. Sometimes, noise walls will not reduce the noise because of the location of the road. Each new road or modification of an existing road that adds capacity must be examined individually to determine what measures can be taken.
SCDOT is continuing to investigate alternative noise abatement measures in North Charleston along the raised structures on I-526 between Virginia Avenue in and I-526. This is due to the costs, complexities and effectiveness of noise barriers on the elevated bridge structures. Other noise abatement measures under consideration include technology to reduce bridge joint noise (like a t-mat bridge expansion joint) and next generation concrete surfaces. According to TXDOT, next generation concrete surface is the quietest and smoothest concrete pavement surface, while maintaining the appropriate friction for safety. To created this next generation concrete surface, traditional diamond grinding is performed. Then, a next generation concrete surface grinding is done to create a uniform profile. Then grooving is done to create negative texture.
Interactive Noise Wall Map
Please click here to open the Interactive Noise Wall map in a new tab ⬈
The map may be navigated using a mouse or keyboard.
If you are unable to view the materials in this interactive noise map, or have questions, please contact the Community Office by calling or texting 843.258.1135.
Answering Your Questions About Highway Traffic Noise
Measures to Reduce Traffic Noise
There are many ways to reduce noise. Noise walls are one tool, but berms and highway design can help reduce noise as well. Sometimes, noise walls will not reduce the noise because of the location of the road. Each new road or modification of an existing road that adds capacity must be examined individually to determine what measures can be taken. This pamphlet will briefly describe how SCDOT determines when noise abatement will be provided and provides contact information if you have more questions. The density of receptors and the distance from the roadway projects are among many factors considered when determining if a noise wall is reasonable and feasible.
When are Noise Walls Considered?
Whenever a highway project uses federal funds and meets the Federal Highway Administration’s (FHWA’s) criteria of a Type I project, the potential for increased traffic noise — and how to reduce it — must be evaluated. For all Type I projects where traffic noise impacts are predicted, noise abatement (typically in the form of noise walls) must be considered.
Potential traffic noise increases are evaluated for any building permitted before the “Date of Public Knowledge.”
The graphics in the pamplet explain:
If there are many houses that have a high density and are close to the road, an acoustic barrier could reduce the noise in many houses.
If there is a low density of houses, that is, there are not many houses and they are not close to each other or to the road, the cost of the acoustic barrier would be high considering that few houses would benefit.
If there are many houses, but they are far from the road, they would be too far away for a wall of noise to reduce noise enough to be considered a wall of noise.
How is Traffic Noise Evaluated?
Using complex computer modeling, we predict expected noise changes at noise-sensitive locations along the project corridor for future traffic conditions.
Then we must determine which noisesensitive locations were permitted before the Date of Public Knowledge and, therefore, are eligible for noise reduction.
If the anticipated noise increase is more than the level defined by SCDOT policy, we begin to consider possible ways to reduce the noise, such as with noise walls and earth berms, at all eligible locations.
What is the “Date of Public Knowledge?”
This is the date that the public (and local government) is notified of the future path of the road and is the date of approval of the Categorical Exclusion (CE), the Finding of No Significant Impact (FONSI), or the Record of Decision (ROD).
Are There Alternatives to Noise Walls?
Other options may also help reduce traffic noise. Some of these may be provided by SCDOT, and others are alternatives that might be considered by private developers or homeowners.Land use design — if homes are set back from the road or are separated from the road by other development, the noise levels may be lower.
Noise berm (earth or other materials) and combination berm/wall systems.
Tiypes of vehicles/speed limits — noise can be reduced with lower speed limits and truck restrictions on a road. However, reducing the speed limit below the appropriate speed based on the design will have only a moderate effect on traffic noise and may actually increase the number of accidents on the roadway.
Building insulation — noise insulation in buildings, such as replacing doors and windows or adding insulation to walls and attics.
How Does SCDOT Decide Which Communities Get Noise Walls?
Once SCDOT has completed the technical evaluation, they also consider the following questions:Will a noise wall reduce the noise enough to justify its construction? Sometimes, a noise wall will not reduce the noise enough to be considered reasonable and/or feasible.
Is a noise wall technically feasible? Every road is different, many factors are considered such as topography, safety, drainage, utilities, maintenance of the wall, and whether driveways and side road access will be impacted.
How many people will hear a difference in noise? Is that number high enough to justify the cost? Sometimes, the cost is too high to build a wall when compared to the benefits received.
Does a simple majority of property owners and tenants who receive a predicted noise level reduction due to construction of a noise wall actually want the wall? Public preference for or against a wall is obtained through a balloting process.
Are alternatives to noise walls available?
When do Noise Walls Work?
Sounds travels very much like water or light. It follows the easiest path over, under, and around things in its path. The further away from the source of the sound, the lower the noise.Noise walls do not work if the source of the noise can be seen. The noise will simply travel through that opening much like water will flow through a crack in a dam. If a building is located higher than a noise wall, the noise will flow over the wall to the building.